BUILD/MINOR: diff: pin version of go method generator #1176

Job	Run time
generate-models	1m 29s
generate-specification	59s
HAProxy check commit message	0s
license-check	0s
go mod tidy	0s
golangci-lint	-1s
Test equal	-1s
lint-spec	-1s
Build	-1s
Tests	-1s
e2e on HAProxy	0s
	2m 23s

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